feat(tts-plugin): complete Plugin Architecture refactor

- Normalize Pipeline public API: create_pipeline(plugin_id, *, lang_code, device)
- EngineConfig: add lang_code field per Architecture Amendment #1
- Kokoro plugin reads config.lang_code (fixes functional regression)
- Static voice catalog in PluginManifest.voices (None = dynamic/VoiceLister)
- get_voices() reads from manifest without creating Engine
- Remove dead kwargs (sample_rate, auto_download, total_steps) from SuperTonic
- Clean up unused imports and dead code in engine implementations
- Fix test expectations for VoiceLister (mock overrides)
- Add clear_preview_pipelines() for resource management

abogen/tts_plugin/host_context.py

@@ -1,46 +1,46 @@
-"""Host context for the TTS Plugin Architecture.
-
-This module defines the HostContext dataclass that provides minimal
-host services to plugins. It is the only interface through which
-plugins can access host functionality.
-"""
-
-from __future__ import annotations
-
-import logging
-from dataclasses import dataclass
-from pathlib import Path
-from typing import Protocol, runtime_checkable
-
-
-@runtime_checkable
-class HttpClient(Protocol):
-    """Protocol for HTTP client provided by host.
-
-    Plugins can use this for network requests (e.g., API-based engines).
-    """
-
-    def get(self, url: str, **kwargs: object) -> object:
-        """Perform an HTTP GET request."""
-        ...
-
-    def post(self, url: str, **kwargs: object) -> object:
-        """Perform an HTTP POST request."""
-        ...
-
-
-@dataclass(frozen=True)
-class HostContext:
-    """Minimal host context provided to plugins.
-
-    Contains only essential host services. No business logic.
-
-    Attributes:
-        config_dir: Directory for API keys, preferences, and configuration.
-        logger: Logger for plugin logging.
-        http_client: HTTP client for network requests.
-    """
-
-    config_dir: Path
-    logger: logging.Logger
-    http_client: HttpClient
+"""Host context for the TTS Plugin Architecture.
+
+This module defines the HostContext dataclass that provides minimal
+host services to plugins. It is the only interface through which
+plugins can access host functionality.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Protocol, runtime_checkable
+
+
+@runtime_checkable
+class HttpClient(Protocol):
+    """Protocol for HTTP client provided by host.
+
+    Plugins can use this for network requests (e.g., API-based engines).
+    """
+
+    def get(self, url: str, **kwargs: object) -> object:
+        """Perform an HTTP GET request."""
+        ...
+
+    def post(self, url: str, **kwargs: object) -> object:
+        """Perform an HTTP POST request."""
+        ...
+
+
+@dataclass(frozen=True)
+class HostContext:
+    """Minimal host context provided to plugins.
+
+    Contains only essential host services. No business logic.
+
+    Attributes:
+        config_dir: Directory for API keys, preferences, and configuration.
+        logger: Logger for plugin logging.
+        http_client: HTTP client for network requests.
+    """
+
+    config_dir: Path
+    logger: logging.Logger
+    http_client: HttpClient